The Stringent Wastewater discharge limits made the process modelling software an inevitable asset to many process-engineering companies. Process modelling provides a better understanding of new plant designing, upgrading the plant, optimizing the existing plants, and improvements in process control. It also helps to select the lowest CAPEX-OPEX solutions, in troubleshooting, to train the stakeholders, and nowadays even used to predict the greenhouse gas footprint of a treatment plant.

The late 1970s to early 1980s can be considered as the golden era of wastewater treatment models. Several research groups worked independently to develop activated sludge process models, resulted in several models with different equations and notations. Initially, they were only steady-state models, which paved the stepping-stone for the development of dynamic models. The International Water Association (IWA) facilitated the acceleration of the model development by combining the models that existed and released the ASM1 (Activated Sludge Model 1). Later ASM1 got modified to ASM2, ASM2d, ASM3, and their modifications. These developments resulted in the birth of many commercial modelling software using these models as such or with some modifications and upgrades thereof. In general, for any wastewater treatment process simulators, the most important aspect lies in its Biological Model.

The wastewater treatment process is generally divided into the primary, secondary, and tertiary stages. The primary stage includes the mechanical systems; the secondary stage is the most important biological treatment stage. The tertiary is the polishing stage including the suspended solids removal, removal of residual organics from the secondary stage, disinfection, and removal of inorganic components.

From a layman’s point of view, a wastewater treatment model can be one or several equations that describe one or several processes that are being functional in a treatment plant. The model can be physical models such as Gravitational settling models (used for primary and secondary clarifiers), Chemical Precipitation models (important for chemical processes such as lime/alum/struvite precipitations), Biological Models (such as for aerobic, anaerobic biological processes), aeration models (important for mass transfer/mixing) or can be filtration models (such as the membrane filtration).

Wastewater usually is not homogenous, the flow (hydraulics) and the concentrations are many times inhomogeneous. wastewater treatment plants, especially the large ones, are not at the luxury to afford a large collection tank. The flow variations could be due to the diurnal changes or rain (monsoon) for instance, similarly, the concentrations load changes could be, due to an industrial discharge. The effect of this heterogenicity, in hydraulic and/or concentration loads, on the treatment plant efficiency can only be predicted using dynamic modelling. Using the model one could investigate the best alternative solution to the problem.

Control systems and control philosophies are absolutely essential in the operation of a wastewater treatment plant economically. When it comes to advanced biological processes, the odds are that the control system is “the heart” of the process. In case of the advanced biological processes, such as a combination of Nitrification-denitrification, Sequential Batch Reactors, granular sludge sequential reactors, Nitritation Deammonification treatment, Sulphur oxidation, Biological/chemical phosphorous removal, etc the treatment efficiency prediction becomes almost impossible without good modelling software. Technically, the simulator helps the process engineer to predict the treatment efficiency.

We at Elixir Enviro Systems Pvt Ltd are proficient in modelling the wastewater treatment plant. We are a distributor of EnviroSim Associates’ BioWin software for the wastewater treatment plants. We also have our own proprietary Anaerobic Digestion model (non-commercial) for the simulation of wastewaters generated from different industries

Should you have any queries, please do connect to us at [email protected]

Anaerobic Treatment

Anaerobic digestion is a biological treatment where the degradation of the organic matter happens in the absence of oxygen and produces biogas as a by-product.  Anaerobic digestion of wastewater is the economic choice for the treatment of high-COD industrial effluents. High-rate anaerobic reactors extend the benefit of anaerobic treatment for medium and high strength effluent, substantially reducing the cost of effluent treatment plants. In an anaerobic digestion, a variety of micro-organisms have to work together to convert organic pollutants into biogas. Biogas contains 50 to 80% methane.

High-Rate Anaerobic Reactors

High-rate reactors operate on the principle of decoupling biomass retention time from the hydraulic retention time. Examples of high-rate anaerobic reactors include the UASB (Up-flow Anaerobic Sludge Blanket) reactor and the Packed Bed Fixed Film reactor and the Fluidized Bed Fixed Film Reactor etc. The hydraulic retention time required for COD removal in high-rate reactors is small. This is important in reducing plant cost for the treatment of medium and high strength effluents which are usually discharged in large quantities.

Complex Wastewaters

Complex wastewaters are the wastewater with having high undissolved or particulate COD. High-rate reactors are successful only for the treatment of effluents containing COD in dissolved form. There are no high-rate reactors, in use, for the treatment of complex wastewaters, i.e., wastewaters containing undissolved COD.  The basic process of anaerobic degradation of complex effluent is:

1. Solubilization and hydrolysis:     Insoluble COD converted to soluble compounds of lower molecular weight such as long chain fatty acids by enzymatic reactions using enzymes secreted by microbes

2. Acidogenesis – reactions that result in the formation of volatile fatty acids from long chain fatty acids – these carried out by acidogenic bacteria

3. Acetogenesis – formation of acetic acid, hydrogen and carbon dioxide from volatile fatty acids

4. Methanogenesis – formation of methane by a) break up of acetic acid b) synthesis from carbon dioxide and hydrogen

In general, or in case of wastewater having high soluble COD, the Methanogenesis turns out to be the rate-limiting step in the anaerobic treatment of wastewaters. On the other hand, Solubilization and hydrolysis are rate limiting in the anaerobic treatment of wastewaters with insoluble COD.

Example:  Dairy Wastewater And Slaughterhouse Wastewater Are Typical Complex Wastewater

Dairy wastewater is a high strength complex industrial waste. Untreated, the waste rapidly putrefies, causing severe odour. Conventional anaerobic reactors are unable to carry out biomethanation of fat in dairy wastewater. Therefore, many a times end up other removal steps for fats and suspended particles discharged along with the wastewater. The characteristics of dairy wastewater greatly depends on the products and dairy operation. For example: Milk effluent has characteristics different from that of cheese effluent or ice-cream effluent.  Special attention has to be given to the following aspects of process and reactor design when dairy wastewaters are to be treated

• Fat content – fat is very slowly degraded in anaerobic reactors. Even after long fat retention time, a non-degraded residual fraction is retained in the reactor and accumulates in the sludge and as scum.
• Acidification – milk effluent is rapidly acidified by breakdown of lactose resulting in acidification. Acidified milk effluent has to be neutralized, by alkali addition or by alkalinity recycle, in order to enable high-rate methanogenesis.
• Coagulation of solids – milk solids are coagulated at low pH. Coagulated solids are more difficult to degrade than emulsified solids.

Hence, the anaerobic process for dairy wastewater is more effective when:

• Effluent is unacidified
• Reactor provides good back-mixing
• Sludge has high fat degradation activity

UASB Reactor Failure When Applied For The Treatment Of Some Dairy Wastewaters

The UASB reactor is an economical solution for the treatment of effluents which have substantially dissolved pollutants. It combines modern high-rate treatment technology with simplicity of design. In the UASB reactor, special gas-liquid-solid separators are mounted which enable collection of biogas and recycle of anaerobic biomass. The avoidance of internal packing in the reactor greatly reduces the cost of reactor construction. The UASB reactor works best when desirable micro-organisms are retained as highly active and fast settling granules. Granular seed sludge is required for quick start-up of such reactors.

But, when UASB is applied to dairy wastewaters, fat content of dairy wastewaters accumulates in the reactor adsorbed on methanogenic sludge and as scum on the gas-liquid interface. Eventually, sludge density is so reduced that catastrophic sludge washout occurs and reactor failure occurs.

The UASB – Back Flush

The UASB Back flush, is a unique solution to the high-rate anaerobic treatment of complex wastewaters. Anaerobic sludge, is retained in the reactor by a special low density granular filter system integrally provided in the reactor. Thus, the separation of sludge and its retention in the reactor is independent of the settleability of sludge.

UASB BackFlush– Principle Of Operation

The key feature of the UASB-BF is the granular bed filter, which retains sludge and effluent solids. The filter bed is kept free from choking by intermittent inverse fluidization, which backflushes retained solids into the reactor mixed liquor. The backflushing of filter bed is accomplished by a periodic release of gas accumulated in the reactor, thereby avoiding extra pumping systems and power consumption. The granular filter bed is constructed from non-degradable Plastic. Therefore, the UASB-BF is able to decouple both solids and biomass retention time from hydraulic retention time, while providing high mass-transfer conditions. The UASB-BF provides the performance of an anaerobic membrane bioreactor without the drawbacks of expensive systems and high-power costs. The UASB-BF retains all microflora – settling, dispersed and slow growing– enabling the development of high activity sludge.

Elixir Enviro Systems has designed several effluent treatment plants with UASB-BF based anaerobic digestion system. We do the process design, the operational optimization and effective implementation of Anerobic digestion of wastewater across the industries and are a market leader for effluent treatment plants. We have successfully implemented several effluent treatment plant with anaerobic digestion system, especially in ice-cream industries, rice-mill industries and dairy to name a few.

Industries like poultry and meat processing companies causes odour nuisance to the neighborhood. There have been several technologies to tackle this situation. The requirement of an exhaust air treatment system is determined on the basis of the size of the facility, the specific processing operations involved, the exhaust air volume, and pollutant load to be treated, and the resulting nuisance potential. Elixir enviro Systems Pvt Ltd (www.elixirenviro.in) is a pioneer in odour control. Elixir Enviro Systems Pvt Ltd designs the required upstream and downstream processes for the effective odour control strategy. The strategies include appropriate ventilation design and pretreatment steps for the optimal operation of the Odour Control Unit(OCU).

What kind of exhaust air treatment system should be used in a slaughterhouse? It could vary for different facilities and is purely decided on case-by-case basis. Here are the commonly used exhaust air treatment systems for slaughterhouses:

Biological Exhaust Air Treatment

Biological elimination of pollutants from air is the most environmental-friendly technique since it ensures minimal use of chemical agents and in many cases, it comes as the lowest lifetime cost alternative compared with other treatment technologies. In biological exhaust air treatment, microorganisms are used to convert odour components to CO2 and H2O.

Bioscrubber

Bioscrubbers are also called Bio-washers. In the Bioscrubber, absorption of air pollutants and the reaction or degradation of the pollutants occurs in two reactors. In the first stage the air is being washed or gets in contact with the air having the pollutant load and the absorbent or the liquid absorbs the pollutant from the air. In the second stage, this absorbent is treated biologically and circulated back to the washing stage. If you look in general, the Bioscrubbers are mainly employed for highly soluble and low volatile compound treatment.

Bio-Trickling Filter

The contaminated air is passed through the packing media made of inert materials. In these filters, a liquid phase is trickled into the media. The pre-humidification can be avoided in the bio-trickling filters as the water phase can provide the moisture for the biomass activity. In Bio-Trickling filters inert materials with chemical stability, low weight and good mechanical properties are preferred. These filters are well aerated systems and the microorganism responsible for the degradation are usually aerobic but deeper into the bed, there is also anaerobic degradation. The flip side of this process is the requirement of micro and macro-nutrient supplementation to assure that the microorganisms are getting enough nutrients for the growth. If this nutrient supplementation is not properly regulated, this can lead to clogging of the unit.

Biofilter

What is biofilter? It is basically a porous layer made up of organic material. It supports the microbial population. The odorous air is forced into the porous layer where the biological degradation takes place. Odor emission is controlled to over 95 percent with biofilters. It should be noted that media moisture content affects the functioning of biofilters. The biofiltration technology is an entrenched odour pollution control technology in various parts of the world.

Chemical Absorption

The solubility behaviour of contents determines the absorption of gas in liquid. In absorption too, the efficiency is determined by adjusting the pH to acidic or alkaline. Hence the absorbers function as chemical scrubbers.

Process Combination

Rather than limiting to one technique, usage of a combination of techniques has proven to be more efficient in slaughterhouse facilities. For example, combination of chemical and biological processes is mostly practiced.

CONCLUSION

Odor emission is an important measure that should be taken by slaughterhouse or meat and poultry processing facilities for the well-being of humans and environment. Elixir Enviro Systems Pvt Ltd is a pioneer in the field of odour control from such industries. Different kinds of cost-effective and highly efficient odor control systems are designed and implemented by the company all over India.